rather use builder in two ways, than sometimes compiler and sometimes
builder
Also makes it possible to reuse builtin code in mom’s to_risc, as both
use builder. The builtin code by directly adding to compiler, the mom
code not.
slot >> reg makes sense, being a slot_to_reg
but . . .
consistently use of << (as meaning assignment , =) also makes sense
allow both and let time tell which makes more sense
